1. Field of the Invention
The present invention relates to a semiconductor integrated circuit of which operation is controlled according to input of a system clock, and more particularly to a semiconductor integrated circuit, which prevents a sharp change in power-supply voltage, and its power-saving control method and power-saving control program.
2. Description of the Related Art
In recent years, it is significant for various types of OA (Office Automation) equipment not to waste energy. Therefore, the OA equipment is provided with a power-saving mode or the like, and when it is not used for a prescribed time, the functions of portions other than necessary minimum portions stop operating so as to fall in a power-saving state, thereby preventing unnecessary power consumption.
A power-saving technology of the above-described type is disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-184495 entitled, “Image processing device”.
The invention of the Japanese Patent Application Laid-Open No. 2001-184495 covers a technology that power consumption can be decreased by independently controlling to stop a clock signal for individual portions when they are in a standby mode or the like and not required.
The invention of the Japanese Patent Application Laid-Open No. 2001-184495 describes that the individual portions can be stopped by independently controlling, but there is a possibility of causing a malfunction if a power-supply voltage drops sharply even if the stop control is executed independently.
According to the prior art, unnecessary power consumption was prevented by simultaneously activating and stopping the system clock for all large-scale functional blocks. Therefore, there was a problem that an abnormal voltage was produced on a power-supply voltage line to deteriorate the quality of the semiconductor integrated circuit because of switching current of a large number of transistors. There was also a problem that a malfunction was apt to occur because of a drop in power-supply voltage.
The present invention has been made in view of the above circumstances and provides a semiconductor integrated circuit, which is divided into prescribed types of functional blocks so as to activate and stop a system clock with prescribed time intervals for the individual divided blocks, and its power-saving control method and power-saving control program.